In recent years, the use of implantable cardiac devices, such as pacemakers and defibrillators, has become increasingly common. Such devices are now used not only to treat and terminate cardiac arrhythmias, such as atrial tachycardia (AT) and atrial fibrillation (AF), but to prevent them altogether.
A common pacing made known as “triggered pacing” allows sequential pacing of the lower chambers (i.e., ventricles) when activity is detected in the upper chambers (i.e., atria). One key to the safe application of triggered pacing is the ability of the device to recognize atrial rates that are too fast for safe ventricular pacing. When the atrial activity results from an arrhythmia such as atrial tachycardia, flutter, or fibrillation, instead of normal sinus rhythm, the device may inappropriately pace at very high rates. Therefore, most pacemakers that pace in triggered modes contain a feature known as “mode switching.” That is, when an abnormally fast atrial rhythm is detected the device switches out of the triggered pacing mode.
One of the common pacing methods which is used to prevent arrhythmias is known as “overdrive pacing.” Overdrive pacing involves sensing a natural pace of the heart and pacing the heart at a slightly increased rate. One particular method, known as Atrial Preference Pacing (APP) is performed by sensing the sinus rate of the heart and pacing the heart, at the atrium, at a rate slightly higher than the sinus rate.
Overdrive pacing, particularly APP, has been relatively successful in preventing arrhythmias. However, it may be difficult for the device to differentiate between sinus pulses and other pathologic cardiac events, such as premature atrial contractions, atrial tachycardia, and atrial flutters and fibrillations, especially when pacing at relatively high rates (e.g., above 100 beats per minute). Therefore, as the sinus rate approaches these high rates, the device may not be able to detect when the patient is experiencing an arrhythmia. As a result, the device may not appropriately switch out of the triggered pacing mode or may not appropriate antiarrhythmia therapy such as anti-tachycardia pacing or atrial defibrillation shocks. Rather, because the device is misidentifying the other cardiac events as sinus pulses, the device may simply further increase the pacing rate.
Accordingly, it is desirable to provide a method for detecting cardiac arrhythmias during overdrive pacing at high rates. In addition, it is desirable to provide a cardiac device capable of detecting arrhythmias during such pacing. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.